Gas discharge lamps contain a gas mixture fill or filling which is excited, by the electrical discharge through the gas, into emission of radiation. Fluorescent lamps additionally have a phosphor coating on the inside of the discharge tube, which coating converts the short-wavelength (typically ultraviolet) radiation produced by the gas discharge into longer wavelength radiation (typically visible light).
For example, lamps whose radiation is intended to cause increased pigmentation of the skin (tanning) or therapeutic effects on localized diseased patches of skin, typically have gas discharge tubes whose emitted spectrum has intensity maxima in the ultraviolet region. Irradiation by the short wavelength ultraviolet B ("UVB"), which is damaging to human skin, must be avoided. This can be achieved by optimization of the gas mixture or fill placed in the discharge tube, and/or by filtering out the UVB component of the emitted radiation. UV-emitting discharge lamps operate by the familiar high pressure mercury vapor discharge, with the addition in the tube interior of metal halide compounds, in order to increase the integrated intensities of emissions in the UV-A wavelength range (315 nanometers to 380 nanometers) relative to the emissions in the UV-B wavelength range (280 nm to 315 nm). This is known from DE-OS 27 18 735 and U.S. Pat. No. 4,155,025.
In the case of lamps with discharge tubes which are used for cosmetic, medical, and technical applications, such as ultraviolet curing of plastics or graphic reproduction technology, and which therefore should have their highest emission intensity in a predetermined spectral range which is a function of the respective application, it is desirable to keep emissions in other spectral ranges as low as possible, since the non-useful emissions represent energy losses and may produce unwanted side-effects. However, not all discharge tubes available in the market satisfy these criteria.
Damage to a patient's health or malfunctions during technical manufacturing processes can be the result.
Further problems can arise, if discharge tubes continue to be used, after expiration of the normal service life specified by the manufacturer. The spectral intensity of the discharge tube may drop off substantially, or shift into other spectral ranges. Generally, the result of such use is unsatisfactory performance, or failure to achieve the expected successful result.